Mission to Mars searches for signatures of life
In the shadow of past failures, probes are set to land today.
More than a century ago, H.G. Wells penned "The War of the Worlds," a tale of technologically advanced Martians that invaded Earth in a quest for water. Today NASA turns the tables with its latest conquest of the Red Planet, this time in the form of a trio of pint-size spacecraft that will prospect for the elusive liquid. Armed with a metal shovel, tiny drills, and chemical detectors, the Mars Polar Lander and a pair of grapefruit-size microprobes will plumb the frozen steppes of Mars' south pole for clues about the planet's mysterious past and present. More important, though, the trio could provide important insights into the ultimate question that has gripped planetary scientists for more than 100 years: Could Mars ever have supported life?
"We are hoping that we can find some trace of water below the surface," says Norm Haynes, former director of the Mars exploration program at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif."It's a critical factor in whether life ever started there."
For NASA, the mission presents an opportunity for redemption. The success of the Polar Lander and its two microprobes could help erase the memory of the failed Mars Climate Orbiter last summer.
But the mission will be a cliffhanger from the start, with an exceedingly small margin of error. The two Deep Space 2 microprobes must survive a 400 m.p.h. impact when they slam into Mars' surface. JPL scientists tested for this smashdown by dropping models out of airplanes and firing them into the ground out of air guns.
Deep Space 2 project manager Sarah Gavit claims the microprobes can handle hitting loose soil or permafrost. A good-size rock, however, would spell disaster.
The Polar Lander, for its part, must enter the Martian atmosphere through a tiny window 6 miles wide and 25 miles long. If controllers plot its trajectory too low or two high, the lander will pass through the atmosphere and into space.
Should the landings succeed, the trio will find themselves in a curious place. The poles of Mars play a crucial role in determining the planet's weather patterns, something that the Polar Lander will study with a battery of instruments.
Unlike the pockmarked equatorial areas explored by the Pathfinder and Viking missions in 1997 and 1975, these unmarred polar surfaces appear to contain fine layers of sediment, possibly composed of ice, CO2, and other elements. This sediment may hold evidence of climate and atmospheric changes on Mars.
"Presumably this is a record of the deposition of ices and sediments during Martian history," says William Hartmann, a geophysicist on the Mars Global Surveyor team. "The question is: Does this record over millions of years show us wild climate changes on Mars?"
To check the sediment composition, the Polar Lander will dig a trench and put samples into an array of solar-powered ovens with its 6-1/2-foot-long robotic arm. The arm wields a toy-size metal shovel and a camera that can snap images of soil down to resolutions as narrow as a human hair. Ovens no bigger than cigarettes will heat the samples to 950 degrees, vaporizing most components and allowing a laser sensor to discern chemical composition.
The Deep Space 2 probes will perform a similar exercise using their own ovens and drill bits to drag in small soil samples.
These microprobes, which NASA views more as engineering experiments than scientific instruments, could prove useful in the future for creating a network of seismic instruments or weather stations across an alien world. Such networks have long been a Holy Grail of scientists confined to observing global planetary phenomena from a single vantage point.
"We have always ... wanted a network of small stations to monitor the conditions on the surface," says Dr. Gavit. "This is very important for understanding the circulation of the atmosphere."
But the most important part of the mission is the search for water - and the signature of organic life.
The Red Planet's candidacy as a lifeboat began in the 1870s, when Italian astronomer Giovanni Schiaparelli claimed to have spotted channels on the planet. Later that century, Percival Lowell, an American businessman and amateur skywatcher, pronounced that an advanced civilization had dug the canals. Novelists including Wells and Edgar Rice Burrows added to the myth, and scientists speculated that Mars was the planet most like Earth, and therefore the most likely to harbor life.
But the first space missions to orbit Mars in the 1960s revealed an empty landscape of craters. Pictures from the Viking missions, however, showed geographic features that closely resembled dried lake beds or rivers. And Pathfinder beamed back images of vast flood plains.
More recently, the Mars Global Surveyor has sent back detailed pictures of river canyons, shorelines, and stark volcanoes. Scientists have speculated that the bygone bodies of water and geothermal activity could have acted as warming agents on Mars, pointing to the tantalizing possibility that several billion years ago Mars was warmer, wetter, and friendlier to life.
"There are strong indications that the climate was different during that time and it changed somewhere very early to the harsh conditions we know today," says Michael Carr, a geophysicist with the US Geological Survey.
Now, if the Polar Lander recovers chemical evidence that an ocean once existed, it could support theories that the planet, at some point, harbored all the important prerequisites for life. Then the question becomes where might life be found today or, if life never developed, why not?
The evidence of previous volcanic activity indicates that geothermal energy may maintain subsurface liquid water aquifers on Mars where life might exist.
(c) Copyright 1999. The Christian Science Publishing Society